The spinal column is a biomechanical structure composed primarily of ligaments, muscles, vertebrae and intervertebral disks. The biomechanical functions of the spine include: (1) support of the body, which involves the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs, (2) complex physiological motion between these parts, and (3) protection of the spinal cord and nerve roots.
As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of older people. Pain associated with such conditions can be relieved by medication and/or surgery. Of course, it is desirable to eliminate the need for major surgery for all individuals, and, in particular, for the elderly.
More particularly, over the years, a variety of intervertebral implants have been developed in an effort to relieve the pain associated with degenerative and dysfunctional disk conditions. For example, U.S. Pat. No. 4,349,921 to Kuntz discloses an intervertebral disk prosthesis.
U.S. Pat. No. 4,714,469 to Kenna discloses a spinal implant that fuses vertebrae to the implant. The implant has a rigid body that fits between the vertebra with a protuberance extending from a vertebral contacting surface and extends into the vertebral body.
U.S. Pat. No. 5,258,031 to Salib et al. discloses another prosthetic disk with a ball that fits into a socket.
U.S. Pat. Nos. 5,425,773 and 5,562,738 are related patents to Boyd et al. that disclose a disk arthroplasty device for replacement of the spinal disk. A ball-and-socket are provided to enable rotation.
U.S. Pat. No. 5,534,029 to Shima discloses an articulated vertebral body spacer with a pair of upper and lower joint pieces inserted between the vertebra. An intermediate layer is provided to allow for movement between the upper joint piece and the lower joint piece.
U.S. Pat. No. 5,782,832 to Larsen et al. discloses a two-piece ball-and-socket spinal implant with upper and lower plates for insertion within the intervertebral space.
U.S. Pat. No. 6,156,067 to Bryan et al. discloses a prosthesis having two plates with a nucleus there between.
None of these solutions provide an implant that restores a wide range of natural movement.
Accordingly, there needs to be developed implants for alleviating such conditions, and for restoring natural movement.